Oilfield applications involve high pressures as well as fluctuating flows and pressures. Thus, when connections need to be made, they need to be able to withstand a variety of different conditions. In the past, various designs incorporating preload into connections have been used. Generally speaking, these connections would involve a tapered ring powered by a hydraulic cylinder or cylinders which would be pulled down on collets having a tapered exterior so as to force the collets against the two pieces being joined. The two pieces would have flanges which would be held together by an internal groove in the collets. Typical of such designs are the model 70 and the high-capacity (HC) collet connectors offered by Cooper Cameron. The high-capacity connector would allow for a preload of 7 million lbs. for 183/4" connections having a 15,000 psi working pressure. One of the drawbacks of such connectors is that they are expensive to construct and their large size makes their assembly in the field more cumbersome. Additionally, such designs require the use of tapered locking surfaces which depend on friction to remain locked. Lubricating components which can appear on the taper of the lock ring or on the outer surface of the collet segments can act to undermine the connection, causing a potential for leakage.
Other designs involving preload in a connection in oilfield use are illustrated in U.S. Pat. Nos. 5,066,048 and 5,247,996. Other connections for subsea use involving the use of dogs in grooves are shown in U.S. Pat. Nos. 5,273,117; 5,163,514; and 4,712,621.
Subsea chokes have been designed with retrievable inserts. The choke body is generally mounted to the Christmas tree or manifold and the insert is a unitized trim cartridge and actuator assembly which can be retrieved to the surface, leaving the choke body subsea. A crown-type connector has been used in such subsea chokes. This design involves a single-piece cylindrical collet with slots machined to form locking fingers. The insert would be pushed into a receptacle and the collet fingers would then move outwardly into an internal groove in the choke body. The operating principle for obtaining the preload in these subsea chokes was similar to the principles relied upon in U.S. Pat. No. 5,066,048. However, the drawback of this design for a retrievable subsea choke was that it was very expensive to manufacture and its large size made it difficult to manipulate it into position in the choke body which remained subsea.
What is desirable is a connection which could provide the requisite preload in subsea choke while being small and cheaper to manufacture. The preload requirement functionally eliminated in the past the use of dog-in-window or groove-type designs, split rings or other types of connectors that didn't have a tapered fit between a locking piston and a locking element.
What was desired and is an objective of the present invention is to provide a simple connection which can give the necessary amount of preload, while combining that design into a compact assembly which would significantly reduce costs compared to previous designs and greatly facilitate installation. Thus, the compactness of the design becomes significant in some instances where room for the connector and actuator for a removable choke insert assembly is in limited supply. Additionally, a more lightweight connector can be more easily manipulated subsea for connection or removal. Another objective was to mount the moving components of the connection on the actuator assembly so that such components do not remain subsea when the connection is undone and the choke insert is removed. While the various configurations of connections are illustrated in this application specifically for a choke with a removable insert, those skilled in the art will appreciate that the objective of the present invention is to provide a connection which can be used in well operations or other applications in the oil and gas industry. Those and other objectives of the present invention will become apparent to those skilled in the art from a review of the description of the preferred embodiment below.